This invention relates in general to locks and more particularly to a key-operated lock which is normally operable by a specific key but may be rendered inoperable as to that key.
Most locks are key-operated, and any person having the proper key may operate the lock to gain access to the area normally secured by it. In some applications it is desirable to have the lock operable by the key at certain times and not operable by that key at other times. For example, some penal institutions assign each inmate a separate cell, yet provide the inmate with a key to that cell, but not to the cell block as a whole, so that the inmate has free acess to the cell block and the various facilities in it. This provides the inmate protection for his personal possessions, and also enable him to remain apart from other inmates if he so desires. Yet there are certain times, such as during periods of rest or disturbances, when the inmates must be confined to their own cells. Hence, the locks on the individual cells must in some way be secured during these periods so that they can no longer be operated by the inmates' keys. Even so, the security personnel must have access to the cells during these periods. Locking arrangements of current design do not provide these capabilities with any degree of simplicity and economy.
A locking arrangement having the foregoing capabilities is useful in other types of buildings. One type of building which would be more easily administered with such a locking arrangement is the typical college dormitory. The student residents of these buildings are provided with keys to the main doors, but the locks cannot be operated by the keys during certain periods of the day.